GB1044514A - Improvements relating to direct current control arrangements - Google Patents

Abstract

1,044,514. Automatic current control. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. May 28, 1963 [June 1, 1962], No. 21243/62. Heading G3R. [Also in Divisions H1 and H2] A direct-current load, such as a traction motor having armature 1A and field winding IF, is connected in series with inductor 2. A device 3 responds at a high level of motor current to disconnect the motor from a D.C. supply and to connect it in a discharge circuit until the current decreases to a low level, whereupon a device 4 reconnects the motor to the supply. As shown, triggering pulses for a silicon controlled rectifier 12 in series with the motor are supplied from the device 4, whilst the discharge circuit comprises diode 13. When the rectifier 12 is rendered conductive, a rectifier 14 is blocked, capacitor 18 being charged through resistor 15. Consequent upon the increase of motor current to the level at which the device 3 responds, rectifier 14 is rendered conductive to discharge the capacitor and to block the rectifier 12. The capacitor 18 is then recharged in the reverse sense until the armature current decreases and causes the device 4 to trigger the rectifier 12. An additional controlled rectifier 16 and resistor 17 may be connected across resistor 15, the rectifiers 12, 16 being triggered simultaneously. This affords stable operation of the rectifier 12 when it is initially rendered conductive. The devices 3, 4, may comprise rings 21, 22 of magnetic material associated with currentcarrying conductor 20. With regard to the device 3, the magnetizing force produced by the motor current is opposed by those due to control current winding 23 and bias current winding 24. Current pulses from generator 19 are supplied to winding 25 to provide a magnetizing force which adds to that due to the motor current. Triggering pulses for the rectifier 14 are derived from the winding 26. The device 4 similarly comprises bias winding 28 whose magnetic force aids that due to the motor current whilst windings 27, 29 act in an opposing sense. Triggering pulses for the rectifiers 12, 16, are derived from the winding 30. The current in windings 23, 27, is zero when the motor is started, the flux in core 21 being varied during each pulse from generator 19 to produce triggering pulses in winding 26. The winding 30 produces no triggering pulses. If the biasing current is now increased, pulses are no longer transmitted to the rectifier 14, and further increase causes rectifiers 12, 16 to become effective to connect the motor to the supply. The build up of motor current then blocks the rectifiers 12, 16, and finally renders the rectifier 14 conductive. The current-responsive means 3, 4 may be replaced by a Hall plate device.